For example, it has been widely known that, when a thin-walled workpiece is cut with a machine tool, there is a problem that chatter vibration occurs on the workpiece due to cutting resistance, and there has been proposed a chuck device which is capable of suppressing such chatter vibration when turning is performed on a thin-walled workpiece, which chuck device is disclosed in Japanese Unexamined Patent Application Publication No. 2012-187688.
This chuck device includes a table and a plurality of clamping means disposed radially on the table, and each clamping means is composed of a first contact means and a second contact means, which are disposed to face each other, and a coupling unit that couples the first contact means with the second contact means. Further, the first contact means includes a pad that is brought into contact with the workpiece, and a bolt that moves the pad toward and away from the workpiece.
When using this chuck device, first, a hollow, cylindrical workpiece is inserted between the first contact means and second contact means of each clamping means. Thereafter, each clamping means is moved outward in a radial direction of the table to bring the second contact means into contact with an inner surface of the workpiece. Subsequently, the bolt of each first contact means is rotated to bring the pad into light contact with an outer surface of the workpiece, and then the workpiece is centered. After the centering, each bolt is further rotated to cause the workpiece to be clamped by the pad and the second contact means. After the workpiece is thus clamped, each clamping means is fixed to a top surface of the table.
Thus, according to this chuck device, because a wall thickness portion of a workpiece is clamped by the first contact means and the second contact means and each clamping means is pressed on and fixed to the top surface of the table, stress and distortion occurring on the workpiece can be minimized, and consequently chatter vibration can be prevented.
However, although the above-described conventional chuck device might be capable of suppressing chatter vibration occurring on a hollow, cylindrical workpiece having a relatively short length, the chuck device cannot exhibit a sufficient damping effect for a hollow, cylindrical workpiece having a long length, because of its configuration.
That is, because the above-described conventional chuck device is configured to clamp an end portion of a workpiece, in the case of a workpiece having a long length, the non-clamped end of the workpiece has a high degree of freedom. Therefore, self-excited vibration is likely to occur, that is, chatter vibration is likely to occur.
Accordingly, in view of this problem, the present applicant has already proposed a damping apparatus disclosed in Japanese Unexamined Patent Application Publication No. 2015-14312.
This damping apparatus is attached around a cylindrical member having a hollow shape to damp vibration of the cylindrical member, and is configured to include a plurality of belt-shaped damping plates that have plasticity and are wounded around the cylindrical member in a state of being laminated together, and a binding band that comprises a band-shaped member having plasticity and is wounded around the plurality of damping plates for binding them together.
According to this damping apparatus, because the damping plates having plasticity are wounded around the cylindrical member and the damping plates are bound together by the binding band, if vibration occurs on the cylindrical member in performing turning on the cylindrical member, the vibration is propagated to the damping plates and thereby each of the damping plates is vibrated, and friction between the damping plates caused by the vibration of the damping plates absorbs the propagated vibration energy, whereby the vibration of the cylindrical member is reduced and damped.
Further, because, as described above, the damping apparatus has the configuration in which the plurality of damping plates having plasticity are wounded around the cylindrical member, the damping apparatus can be arranged at an optimum position along a longitudinal extent of the cylindrical member. Therefore, with respect to a cylindrical member having a long length or a cylindrical member whose vibration state depends on machining conditions, adjusting the arrangement position of the damping apparatus enables the vibration of the cylindrical member to be damped under an optimum state and enables optimization for suppressing chatter vibration. Further, with respect to a cylindrical member having a long length, disposing two or more damping apparatuses enables the vibration of the cylindrical member to be damped more appropriately.